Display device

ABSTRACT

According to an aspect, a display device includes a pixel including: a first sub-pixel including a first color filter transmitting light having a spectrum peak falling on a spectrum of reddish green; a second sub-pixel including a second color filter transmitting light having a spectrum peak failing on a spectrum of bluish green; a third sub-pixel including a third color filter transmitting light having a spectrum peak falling on a spectrum of red; and a fourth sub-pixel including a fourth color filter transmitting light having a spectrum peak falling on a spectrum of blue. The first, second, third, and fourth sub-pixels each include a reflective electrode reflecting light transmitted through the color filter. Each of the third and fourth sub-pixels is greater in size than the first and second sub-pixels. The first sub-pixel with the second sub-pixel has a size equal to or greater than that of the third sub-pixel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Application No.2017-090318, filed on Apr. 28, 2017 and Japanese Application No.2018-028944, filed on Feb. 21, 2018, the contents of which areincorporated by reference herein in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a display device.

2. Description of the Related Art

As disclosed in Japanese Patent Application Laid-open Publication No.2010-97176, a reflective display device that reflects external light todisplay a color image has been known.

The reflective display device typically combines light reflected fromsub-pixels of red (R), green (G), and blue (B) to output light having acolor other than the foregoing colors. However, yellow obtained bycombining reflected light in red (R) and green (G) looks dingy, andobtaining required luminance and saturation has been a difficult task toachieve.

For the foregoing reasons, there is a need for a display device that canenhance the luminance and saturation of yellow.

SUMMARY

According to an aspect, a display device includes: a pixel including: afirst sub-pixel including a color filter that transmits light having aspectrum peak falling on a spectrum of reddish green; a second sub-pixelincluding a second color filter that transmits light having a spectrumpeak falling on a spectrum of bluish green; a third sub-pixel includinga third color filter that transmits light having a spectrum peak fallingon a spectrum of red; and a fourth sub-pixel including a fourth colorfilter that transmits light having a spectrum peak falling on a spectrumof blue. The first sub-pixel, the second sub-pixel, the third sub-pixel,and the fourth sub-pixel each include a reflective electrode thatreflects light transmitted through the corresponding color filter. Eachof the third sub-pixel and the fourth sub-pixel is greater in size thanthe first sub-pixel and the second sib-pixel. The first sub-pixel addedto the second sub-pixel has a size equal to or greater than a size ofthe third sub-pixel.

According to another aspect, a display device includes: a pixelincluding: a first sub-pixel including a first color filter thattransmits light having a spectrum peak falling on a spectrum of reddishgreen; a second sub-pixel including a second color filter that transmitslight having a spectrum peak falling on a spectrum of bluish green; athird sub-pixel including a third color filter that transmits lighthaving a spectrum peak falling on a spectrum of red; and a fourthsub-pixel including a fourth color filter that transmits light having aspectrum peak falling on a spectrum of blue. The first sub-pixel, thesecond sub-pixel, the third sub-pixel, and the fourth sub-pixel eachinclude a reflective electrode that reflects light transmitted throughthe corresponding color filter. Each of the third sub-pixel and thefourth sub-pixel is greater in size than the first sub-pixel and thesecond sub-pixel. The first sub-pixel added to the second sub-pixel hasa size equal to or greater than a size of the third sub-pixel and has asize equal to or greater than a size of the fourth sub-pixel.

According to another aspect, a display device includes: a pixelincluding: a first sub-pixel including a first color filter thattransmits light having a spectrum peak falling on a spectrum of reddishgreen; a second, sub-pixel including a second color filter thattransmits light having a spectrum peak falling on a spectrum of bluishgreen; a third sub-pixel including a third color filter that transmitslight having a spectrum peak falling on a spectrum of red; and a fourthsub-pixel including a fourth color filter that transmits light having aspectrum peak falling on a spectrum of blue. The first sub-pixel, thesecond sub-pixel, the third sub-pixel, and the fourth sub-pixel eachinclude a reflective electrode that reflects light transmitted throughthe corresponding color filter. When the pixel displays yellow havingmaximum luminance, the first sub-pixel, the second sub-pixel, and thethird sub-pixel each exhibit maximum luminance. A total area of thefirst sub-pixel, the second sub-pixel, and the third sub-pixel isgreater than twice an area of the fourth sub-pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating a mainconfiguration of a single sub-pixel;

FIG. 2 is a graph indicating exemplary spectra of red, reddish green,green, bluish green, and, blue;

FIG. 3 is a diagram illustrating exemplary shapes and sizes ofsub-pixels included in a single pixel, an exemplary positional relationamong the sub-pixels, and exemplary color filters of the respectivesub-pixels;

FIG. 4 is a chart indicating relations among reproduced colors by asingle pixel, R, G, and B gradation values applied as image signals, andthe sub-pixels used for the output;

FIG. 5 is a chart indicating a schematic chromaticity diagram (xychromaticity diagram) that represents a correspondence between yellowreproduced by a display device in an embodiment and the peaks of spectraof light transmitted through the color filter, the chromaticity diagrambeing plotted within chromaticity coordinates (xy chromaticitycoordinates);

FIG. 6 is a chart indicating exemplary color reproducibility of theembodiment and that of a comparative example in an L*a*b* color space;

FIG. 7 is a diagram illustrating exemplary shapes and sizes ofsub-pixels included in a single pixel, an exemplary positional relationamong the sub-pixels, and exemplary color filters of the respectivesub-pixels;

FIG. 8 is a diagram illustrating exemplary shapes and sizes ofsub-pixels included in a single pixel, an exemplary positional relationamong the sub-pixels, and exemplary color filters of the respectivesub-pixels;

FIG. 9 is a schematic diagram illustrating, in an sRGB color space, amethod for determining reddish green and bluish green according to anarea ratio of the sub-pixels included in each of different types of asingle pixel;

FIG. 10 is a diagram illustrating an example of dividing each sub-pixelinto a plurality of regions having different areas for area coveragemodulation;

FIG. 11 is a diagram illustrating another example of dividing eachsub-pixel into a plurality of regions having different areas for areacoverage modulation;

FIG. 12 is a diagram illustrating an exemplary circuit configuration ofa display device in the embodiment;

FIG. 13 is a cross-sectional view schematically illustrating asub-divided pixel;

FIG. 14 is a block diagram illustrating an exemplary circuitconfiguration of the pixel employing a memory in pixel (MIP) technology;

FIG. 15 is a timing chart for explaining an operation of the pixelemploying the MIP technology;

FIG. 16 is a block diagram illustrating an exemplary configuration of asignal processing circuit; and

FIG. 17 is a diagram schematically illustrating an exemplary relationamong external light, reflected light, and user's viewpoints when aplurality of display devices are disposed in juxtaposition.

DETAILED DESCRIPTION

Modes (embodiments) for carrying out the present disclosure will bedescribed below in detail with reference to the drawings. The disclosureis given by way of example only, and various changes made withoutdeparting from the spirit of the disclosure and easily conceivable bythose skilled in the art naturally fall within the scope of the presentdisclosure. The drawings may possibly illustrate the width, thethickness, the shape, and other elements of each unit more schematicallythan the actual aspect to simplify the explanation. These elements,however, are given by way of example only and are not intended to limitinterpretation of the present disclosure. In the specification and thedrawings, components similar to those previously described withreference to a preceding drawing are denoted by like reference numerals,and overlapping explanation thereof will be appropriately omitted. Inthis disclosure, when an element A is described as being, “on” anotherelement B, the element A can be directly on the other element B, orthere can be one or more elements between the element A and the otherelement B.

FIG. 1 is a perspective view schematically illustrating a mainconfiguration of a single sub-pixel 15. FIG. 2 is a graph indicatingexemplary spectra of red, reddish green, green, bluish green, and blue.The sub-pixel 15 includes a color filter 20 and a reflective electrode40. The color filter 20 has light transmissivity. The color filter 20has a predetermined peak of a spectrum of light OL to be transmitted outof external light IL. Specifically, the peak of the spectrum of thelight OL to be transmitted through the color filter 20 falls on eitherone of the spectrum of reddish green (e.g., first red green RG1), thespectrum of bluish green (e.g., first blue green BG1), the spectrum ofred (e.g., red R1), and the spectrum of blue (e.g., blue B1). Thereflective electrode 40 reflects the light OL that is transmittedthrough the color filter 20. As exemplified in FIG. 2, the peak of thespectrum of the first red green RG1 and the peak of the spectrum of thefirst blue green BG1 each have a portion overlapping with the peak ofthe spectrum of light viewed as green G. The spectrum of the first redgreen RG1 is closer to the spectrum of the red R1 (on the longwavelength side) than the spectrum of the first blue green BG1 and thespectrum of the green G are. The spectrum of the first blue green BG1 iscloser to the spectrum of the blue B1 (on the short wavelength side)than the spectrum of the first red green RG1 and the spectrum of thegreen G are.

A liquid crystal layer 30 is disposed between the color filter 20 andthe reflective electrode 40. The liquid crystal layer 30 includes liquidcrystal having an orientation determined according to a voltage appliedthereto by the reflective electrode 40, for example. The liquid crystallayer 30 varies a degree of transmission of the light OL that passesbetween the color filter 20 and the reflective electrode 40 according tothe orientation. A light modulation layer 90 may be disposed on theopposite side of the liquid crystal layer 30 across the color filter 20.The light modulation layer 90 modulates, for example, a scatteringdirection of the light OL emitted from the display device.

FIG. 3 is a diagram illustrating exemplary shapes and sizes of thesub-pixels 15 included in a single pixel 10, an exemplary positionalrelation among the sub-pixels 15, and exemplary color filters 20 of therespective sub-pixels 15.

The pixel 10 includes a first sub-pixel 11, a second sub-pixel 12, athird sub-pixel 13, and a fourth sub-pixel 14. The first sub-pixel 11includes a first color filter 20RG1. The second sub-pixel 12 includes asecond color filter 20BG1. The third sub-pixel 13 includes a third colorfilter 20R1. The fourth sub-pixel 14 includes a fourth color filter20B1. The peak of the spectrum of the light transmitted through thefirst color filter 20RG1 falls on the spectrum of the reddish green(first red green RG1). The peak of the spectrum of the light transmittedthrough the second color filter 20BG1 falls on the spectrum of thebluish green (first blue green BG1). The peak of the spectrum of thelight transmitted through the third color filter 20R1 falls on thespectrum of the red (red R1). The peak of the spectrum of the lighttransmitted through the fourth color filter 20B1 falls on the spectrumof the blue (blue B1). The pixel has a square shape in a plan view, andincludes the sub-pixels in the respective four colors in respectiveregions obtained by sectioning the square pixel region. The sub-pixelseach have a square or rectangular shape in a plan view (hereinafterreferred to as a rectangle). The four rectangles are combined to formthe square pixel. A light shielding layer such as a black matrix may bedisposed in regions between the sub-pixels and an outer edge of thepixel, but this light shielding layer occupies only a small area of thepixel. Thus, when describing the shapes or combination of the sub-pixelsor the shape of the pixel, such a light shielding layer may besubstantially disregarded as a linear object constituting an outer edgeof the pixel or the sub-pixel.

In the following description, the term “color filter 20” will be used todescribe the color filter 20 when the peak of the spectrum of the lightOL to be transmitted is not differentiated. When the peak of thespectrum of the light OL to be transmitted is differentiated, the colorfilter 20 will be described as, for example, the first color filter20RG1, the second color filter 20BG1, the third color filter 20R1, orthe fourth color filter 20B1, where appropriate. The light OL that hasbeen transmitted through the color filter 20 is viewed as light in thecolor corresponding to the peak of the spectrum of the light to betransmitted through the color filter 20. The term “sub-pixel 15” will beused when the sub-pixel 15 is not differentiated among the firstsub-pixel 11, the second sub-pixel 12, the third sub-pixel 13, and thefourth sub-pixel 14, for example, by the colors of the color filters 20included in the respective sub-pixels 15. The first sub-pixel 11, thesecond sub-pixel 12, the third sub-pixel 13, and the fourth sub-pixel 14each include the reflective electrode 40 as illustrated in FIG. 1, whichis omitted in FIG. 3.

The third sub-pixel 13 and the fourth sub-pixel 14 are each greater insize than the first sub-pixel 11 and the second sub-pixel 12. The firstsub-pixel 11 added to the second sub-pixel 12 has a size equal to orgreater than a size of the third sub-pixel 13. The fourth sub-pixel 14is greater in size than the third sub-pixel 13. The first sub-pixel 11is identical in size to the second sub-pixel 12. When an area ratio ofthe first sub-pixel 11, the second sub-pixel 12, the third sub-pixel 13,and the fourth sub-pixel 14 is expressed as A to B to C to D, thefollowing expressions hold: 0.65<A=B<1.0, 1.0<C<D, D=4−(A+B+C), andD≤1.7. FIG. 3 exemplifies a case in which the expression of A to B to Cto D=0.744 to 0.744 to 1.130 to 1.382 holds. In this case, the firstsub-pixel 11 added to the second sub-pixel 12 has a size equal to orgreater than a size of the third sub-pixel 13 and has a size equal to orgreater than a size of the fourth sub-pixel 14. In the embodiment, thefirst sub-pixel shares part of a side with the fourth sub-pixel. Incontrast, the second sub-pixel and the third sub-pixel share no side.More specifically, a side shared between the first sub-pixel and thesecond sub-pixel coincides with an intermediate line dividing the pixellaterally into half. In contrast, a side shared between the thirdsub-pixel and the fourth sub-pixel is shifted toward the first sub-pixelwith respect to the intermediate line. As a result, the first sub-pixeland the fourth sub-pixel share part of the side.

FIG. 4 is a chart indicating relations among reproduced colors by asingle pixel, R, G, and B gradation values applied as image signals, andthe sub-pixels used for the output. When the input gradation values ofR, G, and B are expressed as (R, G, B)=(n, n, n), the reproduced coloris white and the first sub-pixel 11, the second sub-pixel 12, the thirdsub-pixel 13, and the fourth sub-pixel 14 are used for the output. Whenthe input gradation values of R, G, and B are expressed as (R, G, B)=(n,0, 0), the reproduced color is red and the third sub-pixel 13 is usedfor the output. When the input gradation values of R, G, and B areexpressed as (R, G, B)=(0, n, 0), the reproduced color is green and thefirst sub-pixel 11 and the second sub-pixel 12 are used for the output.When the input gradation values of R, G, and B are expressed as (R, G,B)=(0, 0, n), the reproduced color is blue and the fourth sub-pixel 14is used for the output. When the input gradation values of R, G, and Bare expressed as (R, G, B)=(m, m, 0), the reproduced color is yellow andthe first sub-pixel 11, the second sub-pixel 12, and the third sub-pixel13 are used for the output. When the input gradation values of R, G, andB are expressed as (R, G, B)=(0, m, m), the reproduced color is cyan andthe first sub-pixel 11, the second sub-pixel 12, and the fourthsub-pixel 14 are used for the output. When the input gradation values ofR, G, and B are expressed as (R, G, B)=(m, 0, m), the reproduced coloris magenta and the third sub-pixel 13 and the fourth sub-pixel 14 areused for the output. In this manner, the display device in theembodiment reproduces yellow through the combination of the firstsub-pixel 11, the second sub-pixel 12, and the third sub-pixel 13. Thedisplay device in the embodiment reproduces green through thecombination of the first sub-pixel 11 and the second sub-pixel 12. Thedisplay device in the embodiment reproduces cyan through the combinationof the first sub-pixel 11, the second sub-pixel 12, and the fourthsub-pixel 14. The display device in the embodiment reproduces magentathrough the combination of the third sub-pixel 13 and the fourthsub-pixel 14. The display device in the embodiment reproduces red usingthe third sub-pixel 13. The display device in the embodiment reproducesblue using the fourth sub-pixel 14.

FIG. 5 is a chart indicating a schematic chromaticity diagram (xychromaticity diagram) that represents a correspondence between yellowreproduced by the display device in the embodiment and the peaks of thespectra of the light OL transmitted through the color filter 20, thechromaticity diagram being plotted within chromaticity coordinates (xychromaticity coordinates). In FIG. 5, the solid-line triangle havingthree vertexes of R, G, and B represents a color space that indicatescolors that can be reproduced by sub-pixels of respective three colorsof the conventional red (R), conventional green (G), and conventionalblue (B) included in the conventional display device, with respect tothe reproduction of yellow Y having predetermined luminance andsaturation required for a display device. Such a conventional displaydevice is unable to reproduce the yellow Y. Specifically, the luminanceand saturation of yellow to be reproduced by the conventional displaydevice are unable to exceed luminance and saturation on a straight lineconnecting the conventional red (R) and the conventional green (G) withrespect to a white point (W), and at least either one of the luminanceand saturation fails to reach the value to reproduce the yellow Y. Evenwhen the conventional display device includes sub-pixels of four colorsof white (W) added to the conventional red (R), the conventional green(G), and the conventional blue (B), increasing saturation of the yellowY using the sub-pixel Of white (W) is a difficult task to achieve.

Trying to reproduce the yellow Y using the sub-pixels of three colors bya conventional technology requires the conventional red (R) and theconventional green (G) to be shifted to red (e.g., R1) and green (e.g.,G1) that can reproduce the yellow Y. However, shifting the conventionalred (R) and the conventional green (G) to the red (e.g., R1) and thegreen (e.g., G1) that can reproduce the yellow Y by simply targeting thereproduction of the yellow Y causes the white point (W) to be shiftedtoward the yellow Y. Specifically, setting the red (e.g., R1) and thegreen (e.g., G1) by targeting the reproduction of the yellow Y in theconventional display device causes a color reproduced by lighting allsub-pixels to be tinged with yellow as a whole, resulting in changingcolor reproducibility. FIG. 5 schematically indicates the white point(W) before being shifted toward the yellow Y using a black dot. FIG. 5further indicates the white point after having been shifted toward theyellow Y using a blank dot outlined by the broken line and denoted asW1. Setting the red (e.g., R1) and the green (e.g., G1) by targeting thereproduction of the yellow Y means to further darken these colors, andreduce light transmission efficiency of the color filter 20 andluminance, resulting in dark yellow.

Trying to achieve the luminance and the saturation corresponding to theyellow Y by adding the yellow sub-pixel to the pixel of the conventionaldisplay device still causes the color reproduced by lighting allsub-pixels to be tinged with yellow as a whole, resulting in changingcolor reproducibility.

In the display device according to the embodiment, on the other hand,the first sub-pixel 11 includes the first color filter 20RG1, and thesecond sub-pixel 12 includes the second color filter 20BG1. The peak ofthe spectrum of the light transmitted through the first color filter20RG1 falls on the spectrum of the reddish green (first red green RG1).The peak of the spectrum of the light transmitted through the secondcolor filter 20BG1 falls on the spectrum of the bluish green (first bluegreen BG1). The peak of the spectrum of the light transmitted throughthe third color filter 20R1 falls on the spectrum of the red (red R1).The peak of the spectrum of the light transmitted through the fourthcolor filter 20B1 falls on the spectrum of the blue (blue B1). Morespecifically, by representing the peak of the spectrum of the light thatpasses through the first color filter on the chromaticity coordinates(RG1 in FIG. 5), the x-coordinate of the peak is between thex-coordinate of the white point and the x-coordinate of the red (R1 inFIG. 5) corresponding to the third color filter 20R1. Similarly, byrepresenting the peak of the spectrum of the light that passes throughthe second color filter on the chromaticity coordinates (BG1 in FIG. 5),the x-coordinate of the peak is between the x-coordinate of the whitepoint and the x-coordinate of the blue (B1 in FIG. 5) corresponding tothe fourth color filter 20B1. Thus, the embodiment obtains a bluecomponent through the second sub-pixel 12 and the fourth sub-pixel 14,thereby preventing the white point (W) from being shifted toward theyellow Y. The embodiment reproduces yellow through the combination ofthe first sub-pixel 11, the second sub-pixel 12, and the third sub-pixel13. Specifically, the peaks of the spectra of light transmitted throughthe first color filter 20RG1, the second color filter 20BG1, and thethird color filter 20R1, respectively, are set such that a combinedcolor of the first red green RG1, the first blue green BG1, and the redR1 is the yellow Y. This configuration allows the yellow Y to bereproduced using the three sub-pixels 15 out of the four sub-pixels 15of the single pixel 10. Thus, the embodiment allows the area of thesub-pixels 15 used for reproducing the yellow Y to be easily increasedas compared with a case in which two colors (R and G) are used out ofthe sub-pixels of three colors of the conventional red (R), theconventional green (G), and the conventional blue (B). Specifically, theembodiment allows larger part of the color filter 20 and the reflectiveelectrode 40 combining the first sub-pixel 11, the second sub-pixel 12,and the third sub-pixel 13 out of a display area of the single pixel 10to be easily allocated to the reproduction of the yellow Y, therebyreliably achieving the luminance and the saturation of the yellow Y.Further, the embodiment also enhances the luminance and the saturationof cyan. Additionally, as compared with a configuration including asub-pixel of white (W), the embodiment allows the third sub-pixel 13including the third color filter 20R1 corresponding to the red (R1) tobe easily enlarged, thereby enhancing the reproducibility of primarycolors.

The embodiment allows the light transmission efficiency of the firstcolor filter 20RG1 transmitting the light whose spectrum peakcorresponds to the reddish green (e.g., first red green RG1) to beeasily increased. Thus, the embodiment uses the first sub-pixel 11including the first color filter 20RG1 for the reproduction of theyellow Y, thereby reliably achieving the luminance and the saturation ofthe yellow Y.

In the display device including the reflective electrode 40 like thedisplay device in the embodiment, a reflection factor and contrast ofthe light OL reflected by the reflective electrode 40 remain constant.Meanwhile, the visual quality of colors of an image output by thedisplay device depends on the light source color and luminous intensityof the external light IL. Thus, when the external light IL is obtainedunder a bright environment, for example, the visual quality of colors ofthe image tends to be good. In contrast, when the external light IL isobtained under a dark environment, it is relatively difficult to exhibitreliable visibility. The color filter 20 does not completely transmitthe external light IL regardless of the peak of the spectrum of thelight OL to be transmitted, and absorbs at least part of the externallight IL. Trying to darken the reproduced color using the color filter20 increases a ratio of an absorbed part of the external light IL. Thus,the display device that outputs an image through reflection of the lightOL by the reflective electrode 40 is required to balance the saturationand the luminance by setting the peaks of the spectra of the light OLtransmitted through the color filters 20 and adjusting an area ratio ofthe color filters 20 having different peaks. In other words, the displaydevice that outputs the image through reflection of the light OL by thereflective electrode 40 has an extreme difficulty in adjusting colorsand luminance by adjusting the light source, which can be achieved by adisplay device having other configurations permitting selection andadjustments of the light source. Application of the present embodimentto even such a display device that outputs the image through reflectionof the light OL by the reflective electrode 40 can still reliably obtainthe luminance and saturation of the yellow Y.

In the embodiment, the area ratio of the first color filter 20RG1, thesecond color filter 20BG1, the third color filter 20R1, and the fourthcolor filter 20B1, and the spectra of the first red green RG1, the firstblue green BG1, the red R1, and the blue B1 are determined depending onthe required white point W and the required luminance and the saturationof the yellow Y. The blue B1 in the embodiment and the conventional blue(B), which are identical to each other in FIG. 5, may be different fromeach other. The red R1 in the embodiment and the conventional red (R),which are identical to each other in FIG. 5, may be different from eachother. Although the combination of the first red green RG1 and the firstblue green BG1 reproduces the conventional green (G) in FIG. 5, thecombination of the first red green RG1 and the first blue green BG1 mayreproduce green that is different from the conventional green (G).

FIG. 6 is a chart indicating exemplary color reproducibility of theembodiment and that of a comparative example in an L*a*b* color space.In FIG. 6, SNAP indicates yellow, green, cyan, blue, magenta, and redspecified. by the Specifications for Newsprint Advertising Production. Adisplay device in the comparative example is an RGBW reflective displaydevice that includes sub-pixels of four colors, i.e., white (W) inaddition to the conventional red (R), the conventional green (G), andthe conventional blue (B). The display device in the embodimentdescribed with reference to FIGS. 1 to 5 can reproduce the yellow Y thatis brighter and more vivid than yellow OY to be reproduced by thedisplay device in the comparative example. The display device in theembodiment can satisfy the demand in advertisement or the like byreproducing the bright and vivid yellow Y as required.

FIG. 7 is a diagram illustrating exemplary shapes and sizes ofsub-pixels 15 included in a single pixel 10A, an exemplary positionalrelation among the sub-pixels 15, and exemplary color filters 20 of therespective sub-pixels 15. FIG. 8 is a diagram illustrating exemplaryshapes and sizes of sub-pixels 15 included in a single pixel 10B, anexemplary positional relation among the sub-pixels 15, and exemplarycolor filters 20 of the respective sub-pixels 15. The display device inthe embodiment may include, in place of the pixel 10 illustrated in FIG.3, the pixel 10A illustrated in FIG. 7 or the pixel 10B illustrated inFIG. 8.

The pixel 10A illustrated in FIG. 7 includes a first sub-pixel 11A, asecond sub-pixel 12A, a third sub-pixel 13A, and a fourth sub-pixel 14A.The first sub-pixel 11A includes a first color filter 20RG2. The secondsub-pixel 12A includes a second color filter 20BG2. The peak of thespectrum of the light transmitted through the first color filter 20RG2falls on the spectrum of the reddish green (second red green RG2). Thepeak of the spectrum of the light transmitted through the second colorfilter 20BG2 falls on the spectrum of the bluish green (second blueGreen RG2). The third sub-pixel 13A includes the third color filter20R1, similarly to the third sub-pixel 13 illustrated in FIG. 3. Thefourth sub-pixel 14A includes the fourth color filter 20B1, similarly tothe fourth sub-pixel 14 illustrated in FIG. 3. The third sub-pixel 13Aand the fourth sub-pixel 14A are each greater in size than the firstsub-pixel 11A and the second sub-pixel 12A. The first sub-pixel 11Aadded to the second sub-pixel 12A has a size equal to or greater than asize of the third sub-pixel 13A and has a size equal to or greater thana size of the fourth sub-pixel 14A. The fourth sub-pixel 14A is greaterin size than the third sub-pixel 13A. The second sub-pixel 12A isgreater in size than the first sub-pixel 11A. When an area ratio of thefirst sub-pixel 11A, the second sub-pixel 12A, the third sub-pixel 13A,and the fourth sub-pixel 14A is expressed as E to F to G to H, thefollowing expressions hold: 0.65≤E<F<1.0, 1.0≤G=H, and H<1.7. Further,the expression of E to F=G to H holds in the example illustrated in FIG.7, but E to F may be a different ratio from that of G to H. Aconfiguration in which the expression of E to F=C to H holds makes iteasy to dispose a signal line 61 and a scanning line 62 (see FIG. 12) ata position corresponding to a boundary between sub-pixels 15 havingdifferent color filters 20. FIG. 7 illustrates an exemplary case inwhich the ratio obtained through rounding each value to the thirddecimal places is expressed as E to F to G to H=0.669 to 0.819 to 1.130to 1.382. In this case, the first sub-pixel 11 added to the secondsub-pixel 12 has a size equal to or greater than a size of the thirdsub-pixel 13 and has a size equal to or greater than a size of thefourth sub-pixel 14. Color reproduction by the pixel 10A illustrated inFIG. 7 can be described by reading the first sub-pixel 11, the secondsub-pixel 12, the third sub-pixel 13, and the fourth sub-pixel 14described with reference to FIG. 4 as the first sub-pixel 11A, thesecond sub-pixel 12A, the third sub-pixel 13A, and the fourth sub-pixel14A, respectively. In such a pixel, the sub-pixels that are diagonallyopposite to each other share no side. More specifically, the pixel isdivided into four regions by one vertical line that divides the pixellaterally and one horizontal line that divides the pixel vertically. Thevertical line is shifted toward the first sub-pixel (left edge side ofthe pixel) with respect to a centerline that laterally divides the pixelinto half. The horizontal line is shifted toward the first sub-pixel(upper edge side of the pixel) with respect to a centerline thatvertically divides the pixel into half. This configuration makes themagnitude relation of E<F≤G<H hold.

The pixel 10B illustrated in FIG. 8 includes a first sub-pixel 11B, asecond sub-pixel 12B, a third sub-pixel 13B, and a fourth sub-pixel 14B.The first sub-pixel 11B includes a first color filter 20RG3. The secondsub-pixel 12B includes a second color filter 20BG3. The peak of thespectrum of the light transmitted through the first color filter 20RG3falls on the spectrum of the reddish green (third red green RG3). Thepeak of the spectrum of the light transmitted through the second colorfilter 20BG3 falls on the spectrum of the bluish green (third blue greenBG3). The third sub-pixel 13B includes the third color filter 20R1,similarly to the third sub-pixel 13 illustrated in FIG. 3. The fourthsub-pixel 14B includes the fourth color filter 20B1, similarly to thefourth sub-pixel 14 illustrated in FIG. 3. The third sub-pixel 13B andthe fourth sub-pixel 14B are each greater in size than the firstsub-pixel 11B and the second sub-pixel 12B. The first sub-pixel 11Badded to the second sub-pixel 12B has a size equal to or greater than asize of the third sub-pixel 13B and has a size equal to or greater thana size of the fourth sub-pixel 14B. The third sub-pixel 13B is identicalin size to the fourth sub-pixel 14B. The first sub-pixel 11B isidentical in size to the second sub-pixel 12B. When an area ratio of thefirst sub-pixel 11B, the second sub-pixel 12B, the third sub-pixel 13B,and the fourth sub-pixel 14B is expressed as I to J to K to L, thefollowing expressions hold: 0.65≤I=J<1.0, and 1.0≤K=L≤1.35. FIG. 8illustrates an exemplary case in which the expression of I to J to K toL=0.744 to 0.744 to 1.256 to 1.256 holds. In this case, the firstsub-pixel 11 added to the second sub-pixel 12 has a size equal to orgreater than a size of the third sub-pixel 13 and has a size equal to orgreater than a size of the fourth sub-pixel 14. Color reproduction bythe pixel 10B illustrated in FIG. 8 can be described by reading thefirst sub-pixel 11, the second sub-pixel 12, the third sub-pixel 13, andthe fourth sub-pixel 14 described with reference to FIG. 4 as the firstsub-pixel 11B, the second sub-pixel 12B, the third sub-pixel 13B, andthe fourth sub-pixel 14B, respectively. In such a pixel, the sub-pixelsthat are diagonally opposite to each other share no side. Morespecifically, the pixel is divided into four regions by one verticalline that divides the pixel laterally and one horizontal line thatdivides the pixel vertically. The vertical line coincides with acenterline that laterally divides the pixel into half. The horizontalline is shifted toward the first sub-pixel (upper edge side of thepixel) with respect to a centerline that vertically divides the pixelinto half. This configuration makes the magnitude relation of I=J<K=Lhold.

FIG. 9 is a schematic diagram illustrating, in an sRGB color space, amethod for determining reddish green and bluish green according to thearea ratio of the sub-pixels 15 included in each of the pixel 10, thepixel 10A, and the pixel 10B. FIG. 9 illustrates a dash-single-dot lineGL that couples the green G, which is a combined color of the first redgreen RG1 and the first blue green BG1, with the white point W, whileillustrating a broken line PL on the yellow side on which a hue angle isin the positive direction with respect to the dash-single-dot line GL.FIG. 9 illustrates a broken line ML on the cyan side on which the hueangle is in the negative direction with respect to the dash-single-dotline GL.

The first sub-pixel 11A of the pixel 10A illustrated in FIG. 7 issmaller in size than the first sub-pixel 11 of the pixel 10 illustratedin FIG. 3. The second sub-pixel 12A of the pixel 10A illustrated in FIG.7 is greater in size than the second sub-pixel 12 of the pixel 10illustrated in FIG. 3. Assume an arrangement in which the color filters20 of the first sub-pixel 11A and the second sub-pixel 12A included inthe pixel 10A illustrated in FIG. 7 are the same as the color filters 20of the first sub-pixel 11 and the second sub-pixel 12 included in thepixel 10 illustrated in FIG. 3. This arrangement decreases the areaallocated to a red component by a relative amount of the reduced firstsub-pixel 11A, and increases the area allocated to a blue component by arelative amount of the enlarged second sub-pixel 12A. As illustrated inFIG. 9, the hue angle of the second red green RG2 corresponding to thepeak of the spectrum of the light transmitted through the first colorfilter 20RG2 included in the first sub-pixel 11A illustrated in FIG. 7is on the positive side relative to the hue angle of the first red greenRG1 corresponding to the peak of the spectrum of the light transmittedthrough the first color filter 20RG1 included in the first sub-pixel 11illustrated in FIG. 3. The hue angle of the second blue green BG2corresponding to the peak of the spectrum of the light transmittedthrough the second color filter 20BG2 included in the second sub-pixel12A illustrated in FIG. 7 is on the positive side relative to the hueangle of the first blue green BG1 corresponding to the peak of thespectrum of the light transmitted through the second color filter 20BG1included in the second sub-pixel 12 illustrated in FIG. 3. Thisconfiguration allows even the pixel 10A illustrated in FIG. 7 to achievethe required yellow Y, white point W, and green G equivalent to those inthe pixel 10 illustrated in FIG. 3.

The third sub-pixel 13B of the pixel 10B illustrated in FIG. 8 isgreater in size than the third sub-pixel 13 of the pixel 10 illustratedin FIG. 3. The fourth sub-pixel 14B of the pixel 10B illustrated in FIG.8 is smaller in size than the fourth sub-pixel 14 of the pixel 10illustrated in FIG. 3. Assume an arrangement in which the color filters20 of the first sub-pixel 11B and the second sub-pixel 12B included inthe pixel 10B illustrated in FIG. 8 are the same as the color filters 20of the first sub-pixel 11 and the second sub-pixel 12 included in thepixel 10 illustrated in FIG. 3. This arrangement increases the areaallocated to the red component by a relative amount of the enlargedthird sub-pixel 13B, and decreases the area allocated to the bluecomponent by a relative amount of the reduced fourth sub-pixel 14B. Asillustrated in FIG. 9, the hue angle of the third red green RG3corresponding to the peak of the spectrum of the light transmittedthrough the first color filter 20RG3 included in the first sub-pixel 11Billustrated in FIG. 8 is on the negative side relative to the hue angleof the first red green RG1 corresponding to the peak of the spectrum ofthe light transmitted through the first color filter 20RG1 included inthe first sub-pixel 11 illustrated in FIG. 3. The hue angle of the thirdblue green BG3 corresponding to the peak of the spectrum of the lighttransmitted through the second color filter 20BG3 included in the secondsub-pixel 12B illustrated in FIG. 8 is on the negative side relative tothe hue angle of the first blue green BG1 corresponding to the peak ofthe spectrum of the light transmitted through the second color filter20BG1 included in the second sub-pixel 12 illustrated in FIG. 3. Thisconfiguration allows even the pixel 10B illustrated in FIG. 8 to achievethe required yellow Y, white point W, and green G equivalent to those inthe pixel 10 illustrated in FIG. 3.

The first red green RG1, the second red green RG2, and the third redgreen RG3 have hue on the positive side with respect to the green G andon the negative side with respect to the red R1. The first blue greenBG1, the second blue green BG2, and the third blue green BG3 have hue onthe negative side with respect to the green G and on the positive sidewith respect to the blue B1.

As exemplified in FIGS. 3, 7, and 8, in the display device in theembodiment, the four sub-pixels 15 included in the single pixel 10, 10A,or 10B have two or more different types of areas. The sub-pixel 15including a color filter 20 having a relatively high luminous efficacyhas a size equal to or smaller than a size of the sub-pixel 15 includinga color filter 20 having a relatively low luminous efficacy.Specifically, the first color filter 20RG1 has a luminous efficacyrelatively higher than a luminous efficacy of the second color filter20BG1. The first color filter 20RG2 has a luminous efficacy relativelyhigher than a luminous efficacy of the second color filter 20BG2. Thefirst color filter 20RG3 has a luminous efficacy relatively higher thana luminous efficacy of the second color filter 20BG3. Further, the firstred green RG1, the second red green RG2, and the third red green RG3,and the first blue green BG1, the second blue green BG2, and the thirdblue green BG3 each have a luminous efficacy relatively higher than aluminous efficacy of the red R1. The red R1 has a luminous efficacyrelatively higher than a luminous efficacy of the blue B1. For thereproduction of yellow, the display device in the embodiment uses threesub-pixels 15 excluding the fourth sub-pixel (e.g., fourth sub-pixel 14)that includes the fourth color filter 20B1. A total area of the threesub-pixels 15 used for reproducing the yellow Y may be equal to orgreater than twice the area of the fourth sub-pixel. Alternatively, thethree sub-pixels other than the fourth sub-pixel may be used toreproduce yellow regardless of the gradation value or the threesub-pixels other than the fourth sub-pixel may be used to reproduceyellow having a predetermined gradation value or higher. The yellowhaving the predetermined gradation value or higher refers to yellowhaving relatively high luminance and saturation as required, that is,yellow exceeding a predetermined halftone. This configuration uses thefirst sub-pixel (e.g., first sub-pixel 11) and the third sub-pixel(e.g., third sub-pixel 13) to reproduce yellow having the halftone orlower.

The sub-pixels 15 having a relatively high luminance efficacy areadjacent to each other in the X-direction or the Y-direction. Forexample, in FIG. 3, the first sub-pixel 11 is adjacent to the secondsub-pixel 12. In FIG. 7, the first sub-pixel 11A is adjacent to thesecond sub-pixel 12A. In FIG. 8, the first sub-pixel 11B is adjacent tothe second sub-pixel 12B.

In the following description, the hue of the light OL transmittedthrough the color filter 20 included in a single sub-pixel 15 isregarded as a reference. The two sub-pixels 15 disposed in juxtapositionto one sub-pixel 15 transmit the light OL having a hue closer to thereference than the remaining one sub-pixel 15 does. The sub-pixels 15are juxtaposed in the X-direction or the Y-direction. For example, inFIG. 3, the hue (first blue green BG1) of the second sub-pixel 12 andthe hue (red R1) of the third sub-pixel 13 are closer to the hue (firstred green RG1) of the first sub-pixel 11 than the hue (blue B1) of thefourth sub-pixel 14 disposed in a diagonal direction of the firstsub-pixel 11 is. The hue (first blue green BG1) of the second sub-pixel12 and the hue (red R1) of the third sub-pixel 13 are closer to the hue(blue B1) of the fourth sub-pixel 14 than the hue (first red green RG1)of the first sub-pixel 11 disposed in a diagonal direction of the fourthsub-pixel 14 is. The diagonal direction extends along the X-Y plane andintersects the X-direction and the Y-direction. Further, the hue (firstred green RG1) of the first sub-pixel 11 and the hue (blue B1) of thefourth sub-pixel 14 are closer to the hue (first blue green BG1) of thesecond sub-pixel 12 than the hue (red R1) of the third sub-pixel 13disposed in a diagonal direction of the second sub-pixel 12 is. The hue(first red green RG1) of the first sub-pixel 11 and the hue (blue B1) ofthe fourth sub-pixel 14 are closer to the hue (red R1) of the thirdsub-pixel 13 than the hue (first blue green BG1) of the second sub-pixel12 disposed in a diagonal direction of the third sub-pixel 13 is.Relations of hues among the sub-pixels 15 illustrated in FIG. 7 can bedescribed by reading the first sub-pixel 11, the second sub-pixel 12,the third sub-pixel 13, and the fourth sub-pixel 14 described withreference to FIG. 3 as the first sub-pixel 11A, the second sub-pixel12A, the third sub-pixel 13A, and the fourth sub-pixel 14A,respectively. Relations of hues among the sub-pixels 15 illustrated inFIG. 8 can be described by reading the first sub-pixel 11, the secondsub-pixel 12, the third sub-pixel 13, and the fourth sub-pixel 14described with reference to FIG. 3 as the first sub-pixel 11B, thesecond sub-pixel 12B, the third sub-pixel 13B, and the fourth sub-pixel14B, respectively.

FIG. 10 is a diagram illustrating an example of dividing each sub-pixel15 into a plurality of regions having different areas for area coveragemodulation. In the display device in the embodiment, a pixel 10Cincludes a first sub-pixel 11C, a second sub-pixel 12C, a thirdsub-pixel 13C, and a fourth sub-pixel 14C, for example, as illustratedin FIG. 10. The first sub-pixel 11C including the first color filter20RG1 includes three regions having different areas including a firstsub-divided pixel 111, a second sub-divided pixel 112, and a thirdsub-divided pixel 113. The first sub-divided pixel 111, the secondsub-divided pixel 112, and the third sub-divided pixel 113 have an arearatio of, for example, 1 to 2 to 4 (=2⁰ to 2¹ to 2²). The firstsub-pixel 11D has gradation performance of three bits (eight gradations)through combinations of whether each of the first sub-divided pixel 111,the second sub-divided pixel 112, and the third sub-divided pixel 113transmits light. More specifically, area coverage modulation performedthrough the combination patters of whether each of the first sub-dividedpixel 111, the second sub-divided. pixel 112, and the third sub-dividedpixel 113 transmits light is expressed as “0 to 0 to 0”, “1 to 0 to 0”,“0 to 1 to 0”, “1 to 1 to 0”, “0 to 0 to 1”, “1 to 0 to 1”, “0 to 1 to1”, and “1 to 1 to 1” in ascending order of an output gradation, where 1denotes that the specific sub-divided pixel transmits light and 0denotes that the specific sub-divided pixel does not transmit light. Ablack. matrix 23 (see FIG. 13) is disposed between the sub-pixels 15.For example, the black matrix 23 is disposed among a plurality of colorfilters 20. For example, the black matrix 23 may be a black filter ormay be configured such that the color filters of two adjacent sub-pixelsare superimposed on top of one another to reduce a transmission factorin the overlapping part. The black matrix 23 may be omitted. A ratio ofarea coverage modulation by the sub-divided pixels (e.g., 1 to 2 to 4)corresponds to an aperture ratio in a plan view. Thus, in aconfiguration including the black matrix 23, the ratio of area coveragemodulation corresponds to a ratio of openings on which the black matrix23 is not disposed. In a configuration without black matrix 23, theratio of area coverage modulation corresponds to an area ratio of thereflective electrodes 40 included in the respective sub-divided pixels.Specific shapes of the reflective electrodes 40 vary depending on howthe sub-pixel is divided. For example, in FIG. 10, the reflectiveelectrodes 40 having a rectangular shape, an L-shape, and an L-shape areprovided from the central side of the pixel 10C with the respectivesub-divided pixels.

The second sub-pixel 12C including the second color filter 20BG1includes a plurality of sub-divided pixels that may be a firstsub-divided pixel 121, a second sub-divided pixel 122, and a thirdsub-divided pixel 123. The third sub-pixel 13C including the third colorfilter 20R1 includes a plurality of sub-divided pixels that may be afirst sub-divided pixel 131, a second sub-divided pixel 132, and a thirdsub-divided pixel 133. The fourth sub-pixel 14C including the fourthcolor filter 20B1 includes a plurality of sub-divided pixels that may bea first sub-divided pixel 141, a second sub-divided pixel 142, and athird sub-divided pixel 143. The second sub-pixel 12C, the thirdsub-pixel 13C, and the fourth sub-pixel 14C each achieve the areacoverage modulation through the same mechanism as that of the firstsub-pixel 11C.

The first sub-pixel 11C, the second sub-pixel 12C, the third. sub-pixel13C, and the fourth sub-pixel 14C are configured in the same manner asthe first sub-pixel 11, the second sub-pixel 12, the third sub-pixel 13,and the fourth sub-pixel 14 described above, respectively, except thatthe first sub-pixel 11C, the second sub-pixel 12C, the third sub-pixel13C, and the fourth sub-pixel 14C each include the sub-divided pixels.The sub-pixels 15 included in the pixel 10A illustrated in FIG. 7 andthe pixel 10B illustrated in FIG. 8 may each he divided into a pluralityof sub-divided pixels like the sub-pixels 15 included in the pixel 10Cillustrated in FIG. 10.

FIG. 11 is a diagram illustrating another example of dividing eachsub-pixel 15 into a plurality of regions having different areas for areacoverage modulation. Shapes and arrangements of the sub-pixels 15exemplified in FIGS. 3, 7, 8, and 10 are illustrative only and can bemodified as appropriate. As illustrated in FIG. 11, for example, a pixel10D includes the sub-pixels 15 including a third sub-pixel 13D, a firstsub-pixel 11D, a second sub-pixel 12D, and a fourth sub-pixel 14Dsequentially arranged from one end side in the X-direction. Thesub-pixels 15 each have a stripe shape. These sub-pixels have widths inthe X-direction, the relation of which is expressed as follows: width ofthe first sub-pixel=width of the second sub-pixel<width of the thirdsub-pixel=width of the fourth sub-pixel. The first sub-pixel 11Dincluding the first color filter 20RG3 includes a plurality ofsub-divided pixels that may be a first sub-divided pixel 11 a, secondsub-divided pixels 11 b, and third sub-divided pixels 11 c. An arearatio among the central first sub-divided pixel 11 a, a pair of theupper and lower second sub-divided pixels 11 b, and a pair of the upperand lower third sub-divided pixels 11 c is, for example, 1 to 2 to 4.The first sub-pixel 11C has gradation performance of three bits (eightgradations) through combinations of whether each of the firstsub-divided pixel 11 a, the second sub-divided pixel 11 b, and the thirdsub-divided pixel 11 c transmits light. The second sub-pixel 12Dincluding the second color filter 20BG3 includes a plurality ofsub-divided pixels that may be a first sub-divided pixel 12 a, secondsub-divided pixels 12 b, and third sub-divided pixels 12 c. The thirdsub-pixel 13D including the third color filter 20R1 includes a pluralityof sub-divided pixels that may be a first sub-divided pixel 13 a, secondsub-divided pixels 13 b, and third sub-divided pixels 13 c. The fourthsub-pixel 14D including the fourth color filter 20B1 includes aplurality of sub-divided pixels that may be a first sub-divided pixel 14a, second sub-divided pixels 14 b, and third sub-divided pixels 14 c.The second sub-pixel 12D, the third sub-pixel 13D, and the fourthsub-pixel 14D each achieve the area coverage modulation through the samemechanism as that of the first sub-pixel 11D.

The first sub-pixel 11D, the second sub-pixel 12D, the third sub-pixel13D, and the fourth sub-pixel 14D are configured in the same manner asthe first sub-pixel 11B, the second sub-pixel 12B, the third sub-pixel13B, and the fourth sub-pixel 14B described above, respectively, exceptthat the first sub-pixel 11D, the second sub-pixel 12D, the thirdsub-pixel 13D, and the fourth sub-pixel 14D each include the sub-dividedpixels. FIG. 11 illustrates a case in which an area ratio among thefirst sub-pixel 11D, the second sub-pixel 12D, the third sub-pixel 13D,and the fourth sub-pixel 14D is the same as that among the firstsub-pixel 11B, the second sub-pixel 12B, the third sub-pixel 13B, andthe fourth sub-pixel 14B illustrated in FIG. 8. However, the presentdisclosure is not limited thereto. The area ratio of the stripe-shapedsub-pixels 15 as illustrated in FIG. 11 may be set to be the same asthat of the first sub-pixel 11, the second sub-pixel 12, the thirdsub-pixel 13, and the fourth sub-pixel 14 illustrated in FIG. 3 or asthat of the first sub-pixel 11A, the second sub-pixel 12A, the thirdsub-pixel 13A, and the fourth sub-pixel 14A illustrated in FIG. 7.Further, in the stripe-shaped sub-pixels 15 as illustrated in FIG. 11,two sub-pixels 15 adjacent to one sub-pixel 15 that serves as areference preferably have a hue closer to the hue of the referencesub-pixel 15 than the hue of the remaining one sub-pixel 15. In theexample illustrated in FIG. 11, the one sub-pixel 15 that serves as thereference is the first sub-pixel 11D or the second sub-pixel 12G.

As described above, the sub-pixels 15 illustrated in FIGS. 10 and 11 areeach divided into a plurality of sub-divided pixels having differentareas. Gradation expression for each of the sub-pixels 15 is performedthrough a combination of whether each of the sub-divided pixelstransmits light. The number of sub-divided pixels included in a singlesub-pixel 15 may be two, or four or more. Gradation performance of asingle sub-pixel 15 in the area coverage modulation is indicated by thenumber of bits (N bits) corresponding to the number (N) of thesub-divided pixels, where N is a natural number of 2 or greater.Assuming that the area of the smallest sub-divided pixel is 1, the q-th(q-th bit) sub-divided pixel from the smallest sub-divided pixel has anarea of 2^((q−1)).

The following describes a detailed configuration of a display device 1in the embodiment with reference to FIGS. 12 to 17. In the descriptionwith reference to FIGS. 12 to 17, one of a plurality of sub-dividedpixels will be referred to as a “sub-divided pixel 50”.

FIG. 12 is a diagram illustrating an exemplary circuit configuration ofthe display device in the embodiment. The X-direction in FIG. 12indicates a row direction of the display device 1, and the Y-directionin FIG. 12 indicates a column direction of the display device 1. Asillustrated in FIG. 12, the sub-divided pixel 50 includes, for example,a pixel transistor 51 employing a thin-film transistor (TFT), a liquidcrystal capacitor 52, and a holding capacitor 53. The pixel transistor51 has a gate electrode coupled with a scanning line 62 (62 ₁, 62 ₂, 62₃, . . . ) and a source electrode coupled with a signal line 61 (61 ₁,61 ₂, 61 ₃, . . . ).

The liquid crystal capacitor 52 denotes a capacitance component of aliquid crystal material generated between the reflective electrode 40provided for each sub-divided pixel 50 and a counter electrode 22 (seeFIG. 13) facing some of or all of the reflective electrodes 40. Thereflective electrode 40 is coupled with a drain electrode of the pixeltransistor 51. A common potential V_(COM) is applied to the counterelectrode 22. The common potential V_(COM) is inverted at predeterminedcycle in order to inversely drive the sub-divided pixel 50 (see FIG.15). The holding capacitor 53 has two electrodes. One of the electrodeshas a potential identical to that of the reflective electrode 40 and theother of the electrodes has a potential identical to that of the counterelectrode 22.

The pixel transistor 51 is coupled with the signal line 61 extending inthe column direction and the scanning line 62 extending in the rowdirection. The sub-divided pixel 50 is at an intersection of the signalline 61 and the scanning line 62 in the display area OA. The signallines 61 (61 ₁, 61 ₂, 61 ₃, . . . ) each have one end coupled with anoutput terminal corresponding to each column of a signal output circuit70. The scanning lines 62 (62 ₁, 62 ₂, 62 ₃, . . . ) each have one endcoupled with an output terminal corresponding to each row of a scanningcircuit 80. The signal lines 61 (61 ₁, 61 ₂, 61 ₃, . . . ) each transmita signal for driving the sub-divided pixels 50, i.e., a video signaloutput from the signal output circuit 70, to the sub-divided pixels 50,on a pixel column by pixel column basis. The scanning lines 62 (62 ₁, 62₂, 62 ₃, . . . ) each transmit a signal for selecting the sub-dividedpixels 50 row by row, i.e., a scanning signal output from the scanningcircuit 80, to each pixel row.

The signal output circuit 70 and the scanning circuit 80 are coupledwith a signal processing circuit 100. The signal processing circuit 100calculates a gradation value (R1, RG, BG, and B1 to be described later)of each of four sub-pixels 15 included in each pixel (e.g., pixel 10)according to the input gradation values of RGB. The signal processingcircuit 100 outputs to the signal output circuit 70 a calculation resultas area coverage modulation signals (Ro, RGo, BGo, and Bo) of eachpixel. The signal output circuit 70 transmits to each sub-divided pixel50 the video signal including the area coverage modulation signals (Ro,RGo, BGo, and Bo). The signal processing circuit 100 also outputs to thesignal output circuit 70 and the scanning circuit 80 clock signals thatsynchronize operations of the signal output circuit 70 and the scanningcircuit 80. The scanning circuit 80 scans the sub-divided pixels 50 insynchronism with the video signal from the signal output circuit 70. Theembodiment may employ a configuration in which the signal output circuit70 and the signal processing circuit 100 are included in a single ICchip 140, or a configuration in which the signal output circuit 70 andthe signal processing circuit 100 are individual circuit chips. FIG. 12illustrates circuit chips including the IC chip 140, in a peripheralregion SA of a first substrate 41 using a Chip-On-Glass (COG) technique.This is merely one example of implementation of the circuit chips, andthe present disclosure is not limited thereto. The circuit chip may bemounted on, for example, a flexible printed circuit (FPC) coupled withthe first substrate 41, using a Chip-On-Film (COF) technique.

FIG. 13 is a cross-sectional view schematically illustrating thesub-divided pixel 50. The reflective electrode 40 faces the counterelectrode 22 with the liquid crystal layer 30 interposed therebetween.The reflective electrode 40 is provided to the first substrate 41.Specifically, wiring including the signal line 61, and an insulationlayer 42 are stacked on a surface of the first substrate 41, the surfacefacing the liquid crystal layer 30. The insulation layer 42 insulatesone wiring from another wiring and from electrodes. The reflectiveelectrode 40 is a film-shaped electrode formed on a surface of theinsulation layer 42. The counter electrode 22 and the color filter 20are disposed on a second substrate 21. Specifically, the color filter 20is disposed on a surface of the second substrate 21, the surface facingthe liquid crystal layer 30. The black matrix 23 is disposed among thecolor filters 20. The counter electrode 22 is a film-shaped electrodeformed on a surface of the color filter 20.

The sub-divided pixel 50 illustrated in FIG. 13 represents one of thesub-divided pixels provided for gradation expression by area coveragemodulation described above with reference to FIGS. 10 and 11.Specifically, each of the sub-divided pixels includes an individualreflective electrode 40. The reflective electrode 40 faces the counterelectrode 22 with the liquid crystal layer 30 interposed therebetween.

The first substrate 41 and the second substrate 21 are, for example,glass substrates that transmit light. The counter electrode 22 transmitslight and is formed of, for example, indium tin oxide (ITO). Thereflective electrode 40 is a metal electrode that is formed of thin filmsilver (Ag), for example, and that reflects light.

The liquid crystal layer 30 is sealed with a sealing material, which isnot illustrated. The sealing material seals the liquid crystal layer 30by bonding the first substrate 41 and the second substrate 21 at theirends. A spacer, which is not illustrated, determines a distance betweenthe reflective electrode 40 and the counter electrode 22. An initialorientation state of liquid crystal molecules of the liquid crystallayer 30 is determined by orientation films (not illustrated) providedto the respective first and second substrates 41 and 21. The liquidcrystal molecules do not transmit light in the initial orientationstate. The state of not transmitting light in the initial orientationstate in which no electric field is applied to the liquid crystal layer30 is referred to as normally black.

The spectrum of the light OL transmitted through the color filter 20illustrated in FIG. 13 has a peak that falls on either one of thespectrum of reddish green, the spectrum of bluish green, the spectrum ofred, and the spectrum of blue, as described with reference to FIGS. 3,7, and 8.

As described above, the display device 1 includes: the first substrate41 provided with the reflective electrode 40; the second substrate 21provided with the color filter 20 and the translucent electrode (counterelectrode 22); and the liquid crystal layer 30 disposed between thereflective electrode 40 and the translucent electrode. As described withreference to FIG. 1, the light modulation layer 90, for example, tomodulate the scattering direction of the light OL emitted from thedisplay device, may be provided to the second substrate 21 on theopposite side of the liquid crystal layer 30. The light modulation layer90 includes, for example, a polarizing plate 91 and a scattering layer92. The polarizing plate 91 faces a display surface. The scatteringlayer 92 is disposed between the polarizing plate 91 and the secondsubstrate 21. The polarizing plate 91 prevents glare by transmittingbeams of light polarized in a specific direction. The scattering layer92 scatters the light OL reflected by the reflective electrode 40.

The display device 1 in the embodiment employs the sub-divided pixel 50according to a memory-in-pixel (MIP) technology to have a memoryfunction. According to the MIP technology, the sub-divided pixel 50 hasa memory to store data, thereby allowing the display device 1 to performdisplay in a memory display mode. The memory display mode allows thegradation of the sub-divided pixel 50 to be digitally displayed based onbinary information (logic “1” and logic “0”) stored in the memory in thesub-divided pixel 50.

FIG. 14 is a block diagram illustrating an exemplary circuitconfiguration of the sub-divided pixel 50 employing the MIP technology.FIG. 15 is a timing chart for explaining an operation of the sub-dividedpixel 50 employing the MIP technology. As illustrated in FIG. 14, thesub-divided pixel 50 includes a drive circuit 58 in addition to theliquid crystal capacitor (liquid crystal cell) 52. The drive circuit 58includes three switching devices 54, 55, and 56 and a latch 57. Thedrive circuit 58 has a static random access memory (SRAM) function. Thesub-divided pixel 50 including the drive circuit 58 is configured tohave the SRAM function.

The switching device 54 has one end coupled with the signal line 61. Theswitching device 54 is turned ON (closed) by a scanning signal ϕVapplied from the scanning circuit 80, so that the drive circuit 58obtains data SIG supplied from the signal output circuit 70 via thesignal line 61. The latch 57 includes inverters 571 and 572. Theinverters 571 and 572 are coupled in parallel with each other indirections opposite to each other. The latch 57 latches a potentialcorresponding to the data SIG obtained through the switching device 54.

A control pulse XFRP having a phase opposite to that of the commonpotential V_(COM) is applied to one terminal of the switching device 55.A control pulse FRP having a phase identical to that of the commonpotential V_(COM) is applied to one terminal of the switching device 56.The switching devices 55 and 56 each have the other terminal coupledwith a common connection node. The common connection node serves as anoutput node N_(out). Either one of the switching devices 55 and 56 isturned ON depending on a polarity of the holding potential of the latch57. Through the foregoing operation, the control pulse FRP or thecontrol pulse XFRP is applied to the reflective electrode 40 while thecommon potential V_(COM) is being applied to the counter electrode 22that generates the liquid crystal capacitor 52.

When the holding potential of the latch 57 has a negative polarity, thepixel potential of the liquid crystal capacitor 52 is in the same phasewith that of the common potential V_(COM), causing no potentialdifference between the reflective electrode 40 and the counter electrode22. Thus, no electric field is generated in the liquid crystal layer 30.Consequently, the liquid crystal molecules are not twisted from theinitial orientation state and the normally black state is maintained. Asa result, light is not transmitted in this sub-divided pixel 50. On theother hand, when the holding potential of the latch 57 has a positivepolarity, the pixel potential of the liquid crystal capacitor 52 is inan opposite phase of that of the common potential V_(COM), causing apotential difference between the reflective electrode 40 and the counterelectrode 22. An electric field then is generated in the liquid crystallayer 30. The electric field causes the liquid crystal molecules to betwisted from the initial orientation state and to change orientationthereof. Thus, light is transmitted in the sub-divided pixel 50 (lighttransmitted state). As described above, in the display device 1, thesub-divided pixels each include a holder (latch 57) that holds apotential variable according to gradation expression.

In each sub-divided pixel 50, the control pulse FRP or the control pulseXFRP is applied to the reflective electrode 40 generating the liquidcrystal capacitor 52 when either one of the switching devices 55 and 56is turned ON depending on the polarity of the holding potential of thelatch 57. Transmission of light is thereby controlled for thesub-divided pixel 50.

The foregoing describes the example in which the sub-divided pixel 50employs the SRAM as a memory incorporated in the sub-divided pixel 50.The SRAM is, however, illustrative only and the embodiment may employother types of memory, for example, a dynamic random access memory(DRAM).

FIG. 16 is a block diagram illustrating an exemplary configuration ofthe signal processing circuit. The signal processing circuit 100includes a first processor 110, a second processor 120, and a look-uptable (LUT) 115. The first processor 110 identifies the gradation values(R1, RG, BG, and B1) of the respective four sub-pixels 15 included ineach pixel (e.g., pixel 10) according to the input gradation values ofR, G, and B. The gradation value of “RG” out of the gradation values(R1, RG, BG, and B1) of the respective four sub-pixels 15 is thegradation value of either one of the first red green RG1, the second redgreen RG2, and the third red green RG3, for example.

Specifically, “RG” corresponds to the peak of the spectrum of the lighttransmitted through the first color filter included in the firstsub-pixel. The gradation value of “BG” is the gradation value of eitherone of, for example, the first blue green BG1, the second blue greenBG2, and the third blue green BG3. Specifically, “BG” corresponds to thepeak of the spectrum of the light transmitted through the second colorfilter included in the second sub-pixel. The gradation value of “R1” isthe gradation value of the red (R1), for example. Specifically, “R1”corresponds to the peak of the spectrum of the light transmitted throughthe third color filter included in the third sub-pixel. Further, thegradation value of “B1” is the gradation value of the blue (B1), forexample. Specifically, “B1” corresponds to the peak of the spectrum ofthe light transmitted through the fourth color filter included in thefourth sub-pixel.

The LUT 115 is table data including the information on the gradationvalues of the respective four sub-pixels 15 predetermined for thegradation values of R, G, and B. The following describes an example inwhich the LUT 115 determines the gradation value of each of the firstsub-pixel 11, the second sub-pixel 12, the third sub-pixel 13, and thefourth sub-pixel 14 illustrated in FIG. 3. The first processor 110refers to the LUT 115 and identifies the gradation values of (R1, RG1,BG1, and B1) corresponding to the input gradation values of R, G, and B.For example, when the input gradation values of R, G, and B areexpressed as (R, G, B)=(n, n, n) as illustrated in FIG. 4, the firstprocessor 110 refers to the LUT 115 and identifies the gradation valuesas (R1, RG1, BG1, B1)=(n1, n2, n3, n4), where (n1, n2, n3, n4) representcolors of the first sub-pixel 11, the second sub-pixel 12, the thirdsub-pixel 13, and the fourth sub-pixel 14 and are gradation values forreproducing colors corresponding to (R, G, B)=(n, n, n). The sameapplies to a case in which the input gradation values of R, G, and B areother gradation values. When the input gradation values of R, G, and Bare expressed as (R, G, B)=(n, 0, 0), the first processor 110 identifiesthe gradation values as (R1, RG1, BG1, B1)=(n, 0, 0, 0). When the inputgradation values of R, G, and B are expressed as (R, G, B)=(0, n, 0),the first processor 110 identifies the gradation values as (R1, RG1,BG1, B1)=(0, n5, n6, 0). When the input gradation values of B, G, and Bare expressed as (R, G, B)=(0, 0, n), the first processor 110 identifiesthe gradation values as (R1, RG1, BG1, B1)=(0, 0, 0, n). When the inputgradation values of R, G, and B are expressed as (R, G, B)=(m, m, 0),the first processor 110 identifies the gradation values as (R1, RG1,BG1, B1)=(m1, m2, m3, 0). When the input gradation values of R, G, and Bare expressed as (R, G, B)=(0, m, m), the first processor 110 identifiesthe gradation values as (R1, RG1, BG1, B1)=(0, m4, m5, m6). When theinput gradation. values of R, G, and B are expressed as (R, G, B)=(m, 0,m), the first processor 110 identifies the gradation values as (R1, RG1,BG1, B1)=(m7, 0, 0, m8).

The second processor 120 outputs to the signal output circuit 70 thearea coverage modulation signals (Ro, RGo, BGo, and Bo) corresponding tothe respective sub-divided pixels associated with the gradation values(R1, RG, BG, and B1) (e.g., R1, RG1, BG1, and B1) of the respective foursub-pixels 15. For example, when the gradation values of the colors of(R1, RG1, BG1, and B1) identified by the first processor 110 are 8-bitnumeric values (0 to 255), the second processor 120 divides the 8-bitnumeric values into 2^(N) segments for conversion into N-bit gradationvalues. When N=3, for example, a correspondence relation between theN-bit gradation values (0 to 7) and the 8-bit gradation values (0 to255) may be classified as follows: 0: 0 to 31; 1: 32 to 63; 2: 64 to 95;3: 96 to 127; 4: 128 to 159 5: 160 to 191; 6: 192 to 223; and 7: 224 to255. The foregoing classification example assumes the gradation valuescorresponding to a linear space ranging from 0 to 1.0 in which thegradation values are not subjected to gamma correction. When the gammacorrection is performed, a classification may be changed. In accordancewith the foregoing correspondence relation, the second processor 120converts the 8-bit numeric values representing the gradation values ofthe colors of (R1, RG1, BG1, and B1) into the corresponding N-bitgradation values. For example the second processor 120 converts thegradation values of (R1, RG1, BG1, B1)=(10, 100, 200, 255) to the areacoverage modulation signals of (Ro, RGo, BGo, Bo)=(0, 4, 6, 7), andoutputs the area coverage modulation signals to the signal outputcircuit 70. The foregoing processing achieves expression of the inputgradation values through the area coverage modulation.

FIG. 17 is a diagram schematically illustrating an exemplary relationamong the external light IL, reflected light OL1, OL2, OL3, and OL4, anduser's viewpoints H1 and H2 when a plurality of display devices 1A and1B are disposed in juxtaposition. Each of the display devices 1A and 1Bis the display device in the embodiment (e.g., display device 1). Thereflected light OL1, OL2, OL3, and OL4 represent beams of light OLhaving exit angles different from each other. As illustrated in FIG. 17,when the display devices 1A and 1B are disposed in juxtaposition, forexample, beams of light OL having different exit angles from the displaydevices 1A and 1B may be viewed even with an incident angle of incidentlight IL on the display device 1A being identical to an incident angleof incident light IL on the display device 1B. In this case, withrespect to the user's viewpoint H1, the reflected light OL from thedisplay device 1A is the reflected light OL1, and the reflected light OLfrom the display device 1B is the reflected light OL3. Which of thereflected light OL1 or the reflected light OL2 from the display device1A is viewed by the user is changed depending on which of the user'sviewpoint H1 or the user's view point H2 is assumed. Similarly, which ofthe reflected light OL3 or the reflected light OL4 from the displaydevice 1B is viewed by the user is changed depending on which of theuser's viewpoint H1 or the user's view point H2 is assumed.Consequently, the exit angle of the light OL viewed by the user may varydepending on conditions, such as how the display devices 1A and 1B aredisposed, and where the user's viewpoint is. Thus, the display device 1Amay be configured differently from the display device 1B withoutdeparting from the scope of the present disclosure. For example, eitherone of the display devices 1A and 1B may employ the area ratio of thefour sub-pixels 15 as illustrated in any one of FIGS. 3, 7, and 8, andthe other of the display devices 1A and 1B may employ the area ratio ofthe four sub-pixels 15 as illustrated in the other one of FIGS. 3, 7,and 8. Alternatively, the correspondence relation between the input(gradation values of R, G, and B) and (R1, RG, BG, and B1) in the LUT115 of the display device 1A may be made different from thecorrespondence relation between the input (gradation values of R, G, andB) and (R1, RG, BG, and B1) in the LUT 115 of the display device 1B.

As described above, in the reflective display device in the embodiment,the third sub-pixel and the fourth sub-pixel are each greater in sizethan the first sub-pixel and the second sub-pixel. The first sub-pixeladded to the second sub-pixel has a size equal to or greater than thesize of the third sub-pixel and has a size equal to or greater than thesize of the fourth sub-pixel. The first sub-pixel includes the thirdcolor filter that has a spectrum peak falling on the spectrum of reddishgreen. The second sub-pixel includes the fourth color filter that has aspectrum peak falling on the spectrum of bluish green. The thirdsub-pixel includes the first color fitter that has a spectrum peakfalling on the spectrum of red. The fourth sub-pixel includes the secondcolor filter that has a spectrum peak falling on the spectrum of blue.The foregoing arrangements can further increase the luminance andsaturation of yellow, thereby reliably achieving the required luminanceand saturation of yellow (e.g., yellow Y).

Making the fourth sub-pixel greater in size than the third sub-pixelallows the hue of the spectrum of light transmitted through the colorfilters included in the first sub-pixel and the second sub-pixel to bemore on the positive side. This configuration allows the lighttransmission efficiency of the color filters included in the firstsub-pixel and the second sub-pixel to be more easily increased.Accordingly, the configuration further increases the luminance andsaturation of yellow, thereby reliably achieving the required luminanceand saturation of yellow (e.g., yellow Y).

Making the second sub-pixel greater in size than the first sub-pixelallows the hue of the spectrum of light transmitted through the colorfilter included in the first sub-pixel to be more on the positive side.This configuration allows the light transmission efficiency of the colorfilter included in the first sub-pixel to be more easily increased.Accordingly, the configuration further increases the luminance andsaturation of yellow, thereby reliably achieving the required luminanceand saturation of yellow (e.g., yellow Y).

The first sub-pixel, the second sub-pixel, and the third sub-pixel incombination reproduce yellow. This configuration car allocate a greaterarea of color filters and reflective electrodes combining the firstsub-pixel, the second sub-pixel, and the third sub-pixel out of thedisplay area of a single pixel to the reproduction of yellow.Consequently, the configuration can reliably achieve the requiredluminance and saturation of yellow (e.g., yellow Y).

The first sub-pixel and the second sub-pixel in combination reproducegreen. This configuration can allocate a greater area of color filtersand reflective electrodes combining the first sub-pixel and the secondsub-pixel out of the display area of a single pixel to the reproductionof green.

The first sub-pixel is adjacent to the second sub-pixel. Thisarrangement allows green to be reproduced more uniformly.

A display device operable with lower power consumption can be providedby the sub-divided pixels performing the area coverage modulation

The sub-divided pixels each include a holder that holds a potentialvariable according to gradation expression. This configuration allowsthe display device to further reduce power consumption.

The present disclosure can naturally provide other advantageous effectsthat are provided by the aspects described in the embodiments above andare clearly defined by the description in the present specification orappropriately conceivable by those skilled in the art.

What is claimed is:
 1. A display device comprising: a plurality ofpixels each consisting of four sub-pixels, the four sub-pixelsincluding: a first sub-pixel including a first color filter thattransmits light having a spectrum peak falling on a spectrum of reddishgreen; a second sub-pixel including a second color filter that transmitslight having a spectrum peak falling on a spectrum of bluish green; athird sub-pixel including a third color filter that transmits lighthaving a spectrum peak falling on a spectrum of red; and a fourthsub-pixel including a fourth color filter that transmits light having aspectrum peak falling on a spectrum of blue, wherein each of a size ofthe third color filter and a size of the fourth color filter is greaterthan a size of the first color filter and a size of the second colorfilter, and a combined size of the size of the first color filter andthe size of the second color filter is equal to or greater than the sizeof the third color filter.
 2. The display device according to claim 1,wherein the combined size of the size of the first color filter and thesize of the second color filter is equal to or greater than the size ofthe fourth color filter.
 3. The display device according to claim 1,wherein the size of the fourth color filter s greater than the size ofthe third color filter.
 4. The display device according to claim 1,wherein the first sub-pixel, the second sub-pixel, the third sub-pixel,and the fourth sub-pixel each include a reflective electrode thatreflects light transmitted through the corresponding color filter. 5.The display device according to claim 4, wherein the first sub-pixel,the second sub-pixel, and the third sub-pixel in combination reproduceyellow.
 6. The display device according to claim 4, wherein the firstsub-pixel and the second sub-pixel in combination reproduce green. 7.The display device according to claim 1, wherein a side of the firstcolor filter in the first sub-pixel is directly adjacent to a side ofthe second color filter in the second sub-pixel.
 8. The display deviceaccording to claim 4, wherein the first sub-pixel, the second sub-pixel,the third sub-pixel, and the fourth sub-pixel are each divided into aplurality of sub-divided pixels having different areas, and N-bitgradation expression is performed through a combination of whether eachof the sub-divided pixels transmits light, where N is a natural numberof 2 or greater.
 9. The display device according to claim 8, whereineach of the sub-divided pixels comprises: a first substrate providedwith the reflective electrodes; a second substrate provided with thecolor filters and a translucent electrode; and a liquid crystal layerdisposed between the reflective electrode and the translucent electrode,wherein each of the sub-divided pixels included in the sub-pixels has aholder that holds a potential variable according to the gradationexpression.
 10. A color filter substrate for a display devicecomprising: a plurality of pixel areas each including four sub-pixelareas, the four sub-pixel areas including: a first sub-pixel area inwhich a first color filter is disposed, the first color filtertransmitting light having a spectrum peak falling on a spectrum ofreddish green; a second sub-pixel area in which a second color filter isdisposed, the second color filter transmitting light having a spectrumpeak falling on a spectrum of bluish green; a third sub-pixel area inwhich a third color filter is disposed, the third color filtertransmitting light having a spectrum peak falling on a spectrum of red;and a fourth sub-pixel area in which a fourth color filter is disposed,the fourth color filter transmitting light having a spectrum peakfalling on a spectrum of blue, wherein, in a plan view, the first colorfilter is in contact with the second color filter, each of the thirdsub-pixel area and the fourth sub-pixel area is greater in size than thefirst sub-pixel area and the second sub-pixel area, and a combined areaof the first sub-pixel area and the second sub-pixel area is equal to orgreater than the third sub-pixel area.
 11. The color filter substratefor a display device according to claim 10, wherein the combined area ofthe first sub-pixel area and the second sub-pixel area is equal to orgreater than the fourth sub-pixel area.
 12. The color filter substratefor a display device according to claim 10, wherein the fourth sub-pixelarea is greater than the third sub-pixel area.